1. Field of Invention
The present invention generally relates to a capacitor structure, and more particularly, to a capacitor in a pixel structure used for the Thin Film Transistor-Liquid Crystal Display (abbreviated as TFT-LCD).
2. Description of Related Art
TFT-LCD is mostly composed of a Thin Film Transistor (abbreviated as TFT) element and a Liquid Crystal Display (abbreviated as LCD) element, wherein the TFT element comprises a plurality of TFT that are disposed in a matrix pattern, and each TFT has a pixel electrode. The TFT mentioned above is formed by stacking the gate, channel layer, source/drain layer on a substrate, and the TFT is used as a switching element for the LCD element.
The operation principle of the TFT element is similar to the operation principle of the traditional semiconductor MOS element, both of them having three electrodes (gate, source and drain). The TFT element is typically categorized into two different types, one is made of the amorphous-silicon (a-Si) material and the other is made of the polysilicon material, and the technique of the a-Si TFT is more matured. The pixel capacitor is generally formed in the process of making the TFT and pixel electrode, so as to control the brightness status of the pixel.
FIG. 1 schematically shows a top view of a conventional capacitor in a pixel structure, and FIG. 2 is a sectional sketch map of the portion from I to I′ in FIG. 1.
Referring to both FIG. 1 and FIG. 2, the conventional capacitor in a pixel structure formed under the pixel electrode 112 comprises a bottom electrode 102, a top electrode 104, and a dielectric layer 108 between the bottom electrode 102 and the top electrode 104. The method for forming the capacitor in a pixel structure comprises the steps of: first, forming a bottom electrode 102 on a substrate 100; then forming a dielectric layer 108 on the bottom electrode 102; then forming a top electrode 104 on the dielectric layer 108, wherein the formed top electrode 104 corresponds to the bottom electrode 102 so as to form a coupling region between the bottom electrode 102 and the top electrode 104; forming a passivation layer 110 for covering the top electrode 104 and the dielectric layer 104; afterwards, pattering the passivation layer 110 for forming an opening 106 so as to partially expose the top electrode 104; and finally forming a pixel electrode 112 between the passivation layer 110 and the opening 106, so that the pixel electrode 112 electrically couples with the top electrode 104. Since the opening 106 is for coupling the top electrode 104 to the pixel electrode 112, therefore, the opening can be defined as a contact region.
The light spot defect generally occurs when a short circuit happens in the capacitor. However, if the electrode line of the defective capacitor is cut off directly, the other pixels on the same electrode line are also impacted, thus causing the weak line problem. Therefore, the design of the conventional capacitor in a pixel structure cannot effectively fix the defect if it is generated.